RFR: 8207345: AArch64: Trampoline generation code reads from uninitialized memory

[Aleksey Shipilev]

On 07/16/2018 06:40 PM, Andrew Haley wrote:
> On 07/16/2018 05:38 PM, Aleksey Shipilev wrote:
>> Your choice, really. I used to frown about conditionals like this all around Hotspot, but then I
>> started to see the appeal: you can clearly see (A && B && C) here, even if A, B, C are not trivial.
>> But structurally, you immediately grasp that if A fails, we don't enter the block; if B fails, we
>> don't enter the block, if C fails, we don't enter the block. It takes some time to read through
>> chain of local variables to reach the same verdict.
> 
> I see.  I tried it, and I think your suggestions do help, and the
> hybrid result is best of all:
> 
>   // We need a trampoline if branches are far.
>   if (far_branches()) {
>     // We don't want to emit a trampoline if C2 is generating dummy
>     // code during its branch shortening phase.
>     CompileTask* task = ciEnv::current()->task();
>     if (task != NULL && is_c2_compile(task->comp_level()) &&
>         Compile::current->in_scratch_emit_size()) {
>       address stub = emit_trampoline_stub(offset(), entry.target());
>       if (stub == NULL) {
>         return NULL; // CodeCache is full
>       }
>     }

Looks good.

-Aleksey


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